Novel discharge lamp and coating

ABSTRACT

A color corrected discharge lamp combination providing an emission with a very desirable color similar to that of an incandescent lamp, but maintaining the efficiency and long life advantages of a discharge lamp. The lamp is similar to a normal high-pressure mercury discharge lamp, but also contains a nonluminescent coating of silica, titania, magnesia or alumina or mixtures thereof on the interior surface of the outer envelope to provide a color-shift and a phosphor mixture coated over the nonluminescent coating. The phosphor mixture substantially comprises 70-90 percent by weight of yttrium vanadate phosphor or yttrium phosphate-vanadate phosphor and 10-30 percent by weight of magnesium fluoro-germanate or magnesium arsenate.

1111 3,825,792 [451' July 23,1974

1 1 NOVEL DISCHARGE LAMP AND COATING [75] Inventors: Ferinand Rokosz, Clifton; Joseph W.

Sausville, Glen Rock, both of NJ [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: July 3, 1973 [21] Appl. No.: 376,254

[52] U,S.Cl ..3l3 /4 87,l17/33.5 L, 252/301.4R

Primary Examiner-James W. Lawrence Assistant ExaminerHarold A. Dixon Attorney, Agent, or FirmR. A. Stoltz [57] ABSTRACT A color corrected discharge lamp combination providing an emission with a very desirable color similar to that of an incandescent lamp, but maintainingthe efficiency and long life advantages of a discharge lamp. The lamp is similar to a normal high-pressure mercury discharge lamp, but also contains a non-luminescent coating of. silica, titania, magnesia or alumina or mixtures thereof on the interior surface of the outer envelope to provide a color-shift and a phosphor mixture coated over the non-luminescent coating. The phosphor mixture substantially comprises 70-90 percent by weight of yttrium vanadate phosphor or yttrium phosphate-vanadate phosphor and 10:30 percent by weight of magnesium fluoro-germanate or magnesium arsenate. v 1

2 Claims, 3 Drawing Figures REF. ENERGY SHEET 2 BF 2 FlG.3

AJU

WAVELENGTH NM NOVEL DISCHARGE LAMP AND COATING BACKGROUND or THE INVENTION been apparent that an improvement in quantity of light was gained, but, where the color of objects viewed under the light source was of importance, the quality of the light emitted from such lamps had shortcomings. This was primarily due to the lack of radiation in the red portion of the visible spectrum. As a result, the use of the high-pressure mercury discharge lamp was primarily limited to applications where lamp efficiency was of prime consideration and source color or color rendition from the source were of minor importance, for example, in highway, street and parking lot lighting.

ture at which the filament is operated and the locus of emissions for different temperatures as plotted on an ICI color diagram is commonly referred to as the black body line." In order to maintain a'reasonable life of an incandescent bulb, such are generally run at less than 3,100K and typically at about 2,900I(. The ICI color system is described in detail in the -Handbook of Colorimetry, by Arthur C. Hardy,'The

Technology Press, Massachusetts Institute of Technology (1936).

Not only were color corrected mercury discharge lamps of the prior art of too high a correlated color temperature (too blue), but the emission of such lamps was also away from the black body line (the magnesium fluorogermanate lamp, for example, was too. green) and therefore inherently provided relatively poor color rendition.

The incandescentlamp, which has abundant emissions in the red portion of the visible spectrum has been in use for along time'and users have become accus- 'to'm'ed to" its'radiation. When the high-pressure mer-.

cury discharge lamp came into use, users compared it with the incandescent lamp, and it became evident that unless the emission spectrum'of the high-pressure mercury lamp was changed, it would never replace incandescent lamps where aesthetics were involved. One

method of modifying the spectrum of the high-pressure mercury discharge lamp is to coat the inner surface of the outer envelope with a phosphor. Such color corrected high-pressure mercury discharge lamps are well known in the art.

U.S. Pat. No. 2,748,303 issued to Thorington on May 29, 1956 disclosed the use of magnesium fluorogermanate phosphor (activated with manganese with a valence of 4 plus). Lamps of this type have been widely used and typicallyprovide a correlated color tempera: ture of about 4,100K. Kelvin with a color rendition index of about43. U.S. Pat. No. 2,615,848 issued to Wells on- Oct. 28, 1952 disclosed a high-pressure mercury lamp using a magnesium arsenate phosphor (also activated with manganese with a valence of 4 plus).

. The magnesium arsenate lamps provide lightof a quality similar to that of themagnesium fluorogermanate coated lamps. U.S. Pat. No. 3,569,762 issued to Levine et al on .Mar. 9, 1971 discloses a high-pressure mercury discharge lamp with an yttrium vanadate phosphor (activated with europium with a valence of 3 plus). Such lamps typically have a correlated .color temperature of about 3,600K and a color rendering index of about 47.

' U.S. Pat. No. 3,661,791 issued to Ropp on May 9, 1972 discloses a method for preparing yttrium phosphatevanadate phosphor (activated with-trivalent europium) to be used with a high-pressure mercury discharge lamp. Lamps using such a ,iphosphor'have emissions I similar to that ofilamp'susing'yttrium'vanadate.

The-internationallyacceptedmethod for standardizing and measuring. the color rendering properties oflig-ht sources is set forth-in the publication of the International 1Commiss.ion on Illumination, identifiedas publication CLLE. .NO'. 13 (Ii-1,32) 1965.

The radiation from'a'nincandescent filament'is' wellknown. The. emission is dependent upon' the tempera-- One method which has been used to lower the correlated color temperature is to use a very-thick coating of phosphor. Using such a thick coating of yttrium vanadate-phosphor, forexample, has reduced the correlated color temperature from approximately 3,600 to approximately 3,440K. Unfortunately, this not only reduces the color rendering index slightly but also dramatically reduces the efficiency.

' Silica layers have been used in high pressure mercury vapor lamps. In U.S. Pat. No; 2,838,705, issued to Hierholzer et al. on June 10, 1958 a silica layer is used between the phosphor and -a silverized'reflector to prevent chemical reactions between the phosphor and the reflector. Silica has also been mixed-with phosphors. In U.S. Pat. No..2,806,968 issued to'Thorington on Sept. 17, 1957, silica is mixed with the phosphor, such that less phosphor is required and the cost of the lamp reduced. (silica being less expensive than the phosphor).

, ,7 SUMMARY OF THE INVENTION It has been discovered that a color corrected highpressure mercury discharge lamp combinationwith an' emission having a color very similar to that of an incandescent lamp, but with the efficiency and long life of a discharge lamp can be obtained using non-luminescent oxide coating of silica, magnesia, titania or alumina (or mixtures thereof) on .the interior surface of the outer envelope with one of certain phosphor mixtures coated over the non-luminescent oxide coating. The phosphor mixtures use a manganese-activated phosphor and a europium-activated phosphor, the manganeseactivated phosphor being at least one of magnesium fluorogermanate and magnesium arsenate, and the europium-activated phosphor being at least one of yttrium phosphate vanadate and yttrium vanadate. The mixture uses about 83 percent by weight of europiumactivated phosphor to 17 percent by weight of manganese-activated phosphor. The combination achieves .a'correlated color temperature of about-3,000K with a color rendering index of about'60.

In particular, it has been discovered that principally .snbmicron particles of. the above mentioned nonluminescentoxides providea color shift which'could not be obtained by varying the percentages in the phosphor blend and this color shift, together with certain phosphor blends, makes possible an incandescent-color high pressure mercury discharge lamp.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference maybe had to the exemplary embodiment shown in the accompanying drawings in which:

FIG. 1 is a side elevational view of a discharge lamp constructed in accordance with the present invention, with part of the outer envelope and are tube broken away;

FIG. 2 illustrates the x,y-chromaticity diagram of the ICI system showing the x,y coordinance of the emissions of various lamps; and

FIG. 3 shows the emission spectrum of the lampof the instant invention, with relative energy plotted against wavelength in nanometers.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown the general arrangement of a high-pressure mercury discharge lamp within which the non-luminescent oxide coating and the phosphor mixture coating of the present invention are utilized. The lamp, generally designated 10, includes an outer light-transmitting envelope 12 which is sealed to a standard mogul base 14. Mounted within the outer envelope 12 and spaced therefrom is an arc tube 16. The are tube 16 is mounted within the outer envelope 12 by conventional frame 18 and a pair of straps 20. Sealed within the arc tube 16 disposed at opposite ends thereof is a pair of tungsten operating electrodes 22 and 24. The electrodes 22 and 24 are sealed to opposite ends of the arc tube 16 by a conventional ribbon seal 26. A starting electrode 28 is also sealed to the arc tube adjacent to electrode 24 by means of ribbon seal 26.

The frame 18 is carried by one of a pair of conventional lead-in conductors 30 which extend through a conventional reentrance stem press 32 connected to mogul base 14, which in turn'is connected to a conventional power source 34 in the well-known manner. The electrodes 22, 24 and 28 are electrically connected to one or the other of the lead-in conductors 30. A starting resistor 36 is connected between one of the lead-in conductors 30 and the starting electrode 28 to the frame 18.

A charge of mercury 38 is contained within the arc tube 16 and this predetermined amount of mercury will, when fully vaporized during normal operation of the lamp provide a predetermined pressure therein. The are tube also contains a small charge of an inert ionizable starting gas.

The non-luminescent oxide coating 40 is'disposed directly on the interior surface of the outer envelope 12. The phosphor mixture 42 is coated over the nonluminescent oxide coating 40 and thus the two layers are provided with the phosphor-mixture layer 42 being on the inside closer to the arc tube and the nonluminescent oxide layer being on the outside and directly on the interior surface of the outer envelope.

The lamp configuration, (other than the nonluminescent oxide and particular phosphor coatings) is essentially conventional and a more detailed description of its operation may be found in the aforemen-' tioned U.S. Pat. No. 2,7,48,303.

Generally, the non-luminescent oxide coating 40 will be from about 0.2 to 2 milligrams (mg) per square centimeter (and typically about 0.5-0.9 mg per square centimeter). Generally, the coating of the phosphor mixture 42 will be from about l-8 mg of phosphor per square centimeter of coated area (and preferably about 2.4-2.8 mg per square centimeter).

The particle size of the non-luminescent oxide coating 42 must be principally of submicron size (it must be principally comprised of particles having an average diameter of less than one micron). It has been found, for example, that silica particles having a 0.025 micron average size (such as Pittsburgh Plate Glasss I-IiSil) provide a satisfactory coating. It has been found that theparticle size is critical and experiments with, for example, titania of a particle size generally greater than 2 microns showed that the desired color shift was not obtained.

FIG. 2 shows the relative emissions of various lamps and also the black body line. Point A represents the emission of a clear (without any phosphor coating) high-pressure mercury lamp. Point B represents the,

emission of a magnesium fluorogermanate lamp with a normal thickness of phosphor coating. Point C represents the emission of a yttrium phosphate-vanadate lamp. Point D represents the emission of the lamp of the instant invention and Point E represents the emission of a typical incandescent lamp. The line FG is the black body line. The filament temperatures for various points along the black body line'are as indicated. As noted previously, the emission of the magnesium arsenate lamp is similar to that of the magnesium fluorogermanate lamp and the emission of the yttrium vanadate is similar to that of the yttrium phosphate-vanadate lamp.

Emissions along the line AC can be obtained by using thinner layers of yttrium vanadate phosphor, and emissions along the line AB can be obtained by using thinner coatingsof a vanadate phosphor. Emissions along the line BC can be obtained by a normal coating thickness with a mixture-of vanadate and fluorogermanate phosphors. Similarly, points in the triangle ABC can be achieved by thinner layers of mixtures of these phosphors. Points beyond B along the extension of line AB could'be obtained by a thicker coating of vanadate phosphor, but such thick coatings severely reduce luminous efficiency and, because of the cost of the phosphors, significantly raise the cost of the lamp. Suprisingly, an approximately normal thickness of an appropriate mixture of phosphor produces an emission, not inside triangle ABC, but at point D when the appropriate layer of non-luminescent oxide is included.

The relatively inexpensive layer of non-luminescent oxide such as silica deposited on the interior surface of the outer envelope (between the phosphor mixture and the outer envelope) provides a significant shift in the color of the emission. An emission with a color temperature of about 3,000I( in close-proximity to the black body line can be obtained using normal phosphor thicknesses. When a proper blend (about 90 percent by weight of either yttrium phosphate-vanadate or yttrium vanadate or mixtures of the two is blended with about 10-30 percent by weight of either magnesium fluorogermanate or magnesium arsenate or mixtures of these two) is placed over a layer of appropriate non- 400 watt high-pressure mercury discharge lamp, the result is a lamp emitting approximately 19,500.20,000 lumens after 100 hours of burning with a source 'chromaticity of an incandescent lamp. It was found that mixing the non-luminescent oxide with the phosphors into a single layer coating did not produce the desired color shift but that the deposition of the nonluminescent oxide and phosphors in separate layers provided a color shift (for all light leaving the lamp) and the desired color shift was obtained.

' A coating'of silica can be done, for example, by mixing approximately 39 grams of submicron size silica, together with 170 milliliters of nitrocellulose lacquer and 85 milliliters of butylacetate solvent. Thisslurry is milled for about 3 /2 hours and then coated on the bulb. The bulb is then lehred to remove the lacquer binder. After lehring of the silica coating, the phosphor mixture is applied. A first slurry is prepared by mixing 1,200 grams of yttrium phosphate-vanadate or yttrium vanadate phosphor (preferably yttrium phosphatevanadate) with 775 milliliters of butylacetate solvent and 825 milliliters of nitrocellulose lacquer. A second slurry is prepared by mixing 1,200 grams of magnesium fluorogermanate or magnesium arsenate (preferably magnesium fluorogermanate) with 1,475 milliliters of nitrocellulose lacquer and 600 milliliters of butylacetate solvent. After milling, two slurrie's can be mixed together to a ratio of 1 part by volume of magnesiumfluorogermanate to 4 parts of yttrium phosphatevanadate and coated on the bulb. The coated bulb is then lehred again to remove the binder. The phosphor mixture which results from this coating process is the preferred'mixture and consists essentially of about 17 percent by weight yttrium phosphate-vanadate and about 83 percent by weight of magnesium fluorogermanate.

Magnesia, titania and alumina or mixtures thereof can 'be substituted in whole or in part for the silica in the preceding examples in approximately the same proportions. Alumina is especially convenient as it does not readily absorb moisture (as compared to magnesia or silica) and is readily obtained in submicron size particles (as compared to titania which is generally available only in particle sizes too large for this application).

FIG. 3 illustrates the emission spectrum of a lamp of the instant invention. Such a lamp has enough emission in the 600-700 manometer region to provide enough red to give an incandescent color, but has very little emission in the infrared region (above approximately 700 manometers). Conversely, the incandescent lamp emits-most of its energy in the infrared region, and this energy is generally wasted (and any attempt to get more of the energy in the visible region by raising the filament temperature will, of course, result in further shortening the already relatively short life of the incandescent lamp). Thus, the lamp of the instant invention provides the color of the incandescent lamp, without the low efficiency and short life of the incandescent lamp.

Since numerous changes may be made in the above described high-pressure mercury discharge lamp with its prescribed non-luminescent oxide and phosphor mixture coatings, and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In combination with a discharge lamp-comprising an elongated light-transmitting arc tube containing a predetermined amount of mercury which when fully vaporized during normal operation of said lamp will provide a predetermined pressure of mercury vapor therein, and an outer light-transmitting envelope having an-interior surface spaced from and enclosing said arc tube, the improvement which comprises:

a. a coating of, principally submicron particles of at least one non-luminescent oxide selected from the group consisting of silica, magnesia, titania," and alumina disposed directly on said interior surface of said outer envelope; and b. a phosphor mixture disposed on said nonluminescent oxide coating, said phosphor mixture substantially comprising: I -90 percent by weight of at least one phosphor selected from the group consisting of yttrium phosphate-vanadate activated by europium and yttrium vanadate activated by europium; and

II 10-30 percent by weight of at least one phosphor selected from the group consisting of magnesium fluorogermanate activated with manganese and magnesium arsenate activated with manganese. 2, The combination of claim 1, wherein said phosphor mixture consists essentially of about 83 percent by weight yttrium phosphate-vanadate activated by eruopeum and about 17 percent by weight of magnesium fluorogermanate activated with manganese.

Patent No. 3,825,792 Dated Julv 21.37 4

mwmww) Ferdinand Rokosz and Joseph W. Sausville It is certified that m rror appears in the above-identified patent mad that mid Lemma Patent are herehy eomeciteafi m who On the cover sheet of the patent, the inventors name should be changed from "Fer'inand" to --Fer-dinahd-.

Signedand sealed this 29th day of October 1974.

(SEAL) Attesta MQCOY.MQ GIBSON JR, '0. MARSHALL- DANN At'testlmg Officer Commissioner of Patents FORM Po-wso H0459) UlICOMM-DC eons-P00 \IJ). IIOVIIIIIMI 'llml" O'IICI I. 0-1.0-16 

2. The combination of claim 1, wherein said phosphor mixture consists essentially of about 83 percent by weight yttrium phosphate-vanadate actiVated by eruopeum and about 17 percent by weight of magnesium fluorogermanate activated with manganese. 